Hot runner mould

33 An example of a hot-runner mould an insulated runner mould with heated probes (after Modern Plastics Encyclopedia). 

It is obviously inefficient to take a fresh impression of the sprue and runners (see Fig. 7.28) for each cycle  

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This is similar in concept to the hot runner mould system. In this case, instead of having a specially heated manifold in the mould, large runners (13-25 mm diameter) are used. The relatively cold mould causes a frozen skin to form in... 

The use of the hot runner technique for feeding multi-impression and large area mouldings is now firmly established. The advantages of hot runner mouldings are as follows ... 

In designing hot runner moulds the following important points should be observed ... 

High heat bushings, valve seats, ball valve seats, contact seals, insulator bushings. .. Thermal isolators, high heat insulator bushings for hot runner plastic injection moulds... Guide rollers. .. 

Injection Molten polymer flows into the injection cavity via the hot runner block, to produce the desired shape of the preform with a mandrel (the core pin) producing the inner diameter and the injection cavity the outer. After a set time the injection moulds and core pins part and the preform held in a neck carrier is rotated 90°. 

Frenkel, D. Zawistowski, H., Hot Runners in Injection Moulds, Rapra, Shawbury, 2001. 

The process is injection moulding, using an eight-impression tool, with hot runners to minimize scrap. No reground material is permitted. 

The acetal spring is manufactured by injection moulding. A two-impression tool is used. Although hot runners are often used for acetal, the extra tooling cost is not warrented in this case, and the approximately 20% sprue scrap is re-used. 

For the injection moulding of the plastic parts, hot runners allow a waste free production. The plastic is injection moulded as in a conventional process. When sufficient solidification is reached, the mould opens, and an index plate (this is a rotating platen which takes the plastic parts from the first cavity and puts them into the liquid rubber cavity by rotating them through 180 degrees), robot, etc., extracts the plastic moulding and transfers it into the silicone cavity. 

In the meagre selection of works on the subject of the design of injection moulds, comparatively little space is devoted to hot runner systems. There is only one book exclusively addressing this subject, and that was published in 1960 [E. Moslo, Runnerless Moulding, Reinhold Publishing Corporation, I960]. 

Mould operations may run into problems if trained staff are not available. Start-up of the HR system, change of plastic, stopping and, if necessary, cleaning of hot runners cannot be done without some knowledge and observance of certain principles. For the same reason, repairs and maintenance should be carried out by trained staff only. Damage to moulds caused by unskilled servicing generally leads to serious financial losses. 

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